Laboratory Methods of Inorganic Chemistry, 2nd English Ed. 1928

64 SIMPLE COMPOUNDS.

If, as before, i> represents the volume of the gas-mixture, and the formulas
inclosed in parentheses the number of gram-molecules of substance present
when equilibrium is reached, then for a given temperature the mass-action
law gives the relation:
(SO 3 )'

(SO 2 )^2 (0,) "'

v^1 v

and the "efficiency" of the reaction, i.e., the ratio of the trioxide formed to the
unchanged dioxide, is:
(SO,) <K(OJ
(SOa) \ v '
It is evident from this last expression, that it is favorable to the yield if as
pure oxygen as possible (small v, little diluent of indifferent gas) and as much
oxygen as possible (high concentration of O 2 ) is present. That this conclusion
is correct is shown by the following table, in which the yield (i.e., the actual
quantity of SO 3 obtained, compared with what would result if the entire
amount of the SO 2 could be oxidized) is given in per cent by volume. In the
first case a mixture composed of the theoretically correct proportions of sul-
phur dioxide and oxygen was taken, in the second the same mixture diluted
with nitrogen, and in the third case sulphur dioxide together with an excess of
oxygen. The measurements were made at 500°.

1

2

3

Per cent N 2.

0.

89.50

0.

Per cent SO 2.

66.67

7.00

7.00

Per cent O 2.

33.33

3.5

93.00

Yield in per cerit

SO 2 oxidized.

91.3

81.2

98.1

For the formation of ammonia from the elements:

N 2 + 3H 2 #2 NH 3

the mass-action law gives:

(NH 3 )

2

V V^3

The equilibrium quantity of ammonia is:

(NH 3 ) =

The yield of ammonia, therefore, increases with decreasing volume,